> > > > > What are the flaws and limitations you had in mind?
> > > >
> > > > 1. That all rows of a table have the same number of columns
> > > > which leads to the need for NULLs.
> > >
> > > There is nothing about relations that require nulls.
> >
> > Yet they routinely occurs in practice.
>
> They occur in SQL. They do not occur in the relational model.
In the rdb model, each tuple(row) of a relation(table) must be of the
same degree(number of columns). Thus if we have a column for Social
Security Number, and the person is an illegal immigrant, we will enter
NULL (or some arbitrary code). It is the rdb model which requires each
tuple to have the same degree which does not match reality. In
reality, things need not have the same number of attributes.
Received on Sun May 04 2003 - 18:34:14 CDT
